Gasification of coal in fixed bed reactors is well-known. The British patent to Bailey (supra) discloses coal gasification first in a moving bed reactor and then in a fixed bed reactor. Although a fixed bed reactor provides for virtually complete gasification of coal, it is subject to certain limitations, one being that agglomerating or caking coals that have Free Swelling Indexes in excess of three cannot be tolerated, and another being that agglomerating coal sized with more than 20% by weight of less than 1/4 inch cannot be used. The object of this invention is to provide a process wherein coals having Free Swelling Indexes in excess of three and up to nine are first processed through a moving bed reactor so as to produce hot non-agglomerating char of substantially larger size than it was as raw feed stock for the fixed bed reactor.
If the agglomerating coal containing more than 20% minus 1/4 inch size is fed to a conventional fixed bed reactor, the air and/or oxygen and steam fed to the reactor and the gases produced by the reaction cannot uniformly permeate the bed, and gas production rate and heating value thereby diminish to unacceptable levels. Channelization of the gases occurs and the resultant non-uniform bed causes further operating difficulties to the point of making the operation unfeasible. According to the subject process, however, agglomerating coals containing up to 70% of minus 1/4 inch size can be charged into the first stage reactor and, with proper placement and distribution of air and/or oxygen and steam through the bed, char lumps are produced so as to provide properly sized feed stock for the second stage reactor.
While Bailey (supra) discloses gas take-off from a fixed bed gasifier which is fed with hot coke falling from a moving bed reactor, certain inherent problems limit the transportation of the gas output to a very short distance without cooling the gas and forcing the cooled gas with a fan. The moving bed reactor is normally operated at about atmospheric pressure and hence it was impossible to pressurize the fixed bed reactor without pressurizing the moving bed reactor. The object now is to provide for feeding hot char from a moving bed reactor through a lock hopper which permits the moving bed reactor to operate at about atmosphere pressure and the fixed bed reactor to be pressurized to as to force the gas produced therein to a remote device. For versatility is is intended to provide for deriving the gas outputs from the first and second stage reactors either in a single common stream or in separate mutually exclusive streams.